1. Field
Communication systems, such as third generation partnership project (3GPP) high speed packet access plus (HSPA+), multiple-input multiple-output (MIMO), imbalanced transmission, and advanced receivers thereof may benefit from an HSPA MIMO receiver configured for receipt of an imbalanced transmit signal. A communications device or modem chip can incorporate such a configuration.
2. Description of the Related Art
A conventional linear minimum mean square error (LMMSE)-based chip equalizer may assume that two transmit antennas have equal transmit power. As such, scaling factors may not be used. Additionally, an ad hoc solution may be used for the diagonal loading factor instead of an accurate noise variance estimate σηi2. Mathematically, the conventional solution can be expressed as follows:{tilde over (w)}LMMSE,1=(Ĥ1Ĥ1H+Ĥ2Ĥ2H+KI2F)−1Ĥ1δD,{tilde over (w)}LMMSE,2=(Ĥ1Ĥ1H+Ĥ2Ĥ2H+KI2F)−1Ĥ2δD where {tilde over (w)}LMMSE,i, i=1,2 are the LMMSE equalizer filter coefficients, Ĥi, i=1,2 are the channel matrixes constructed from the channel impulse response estimates, with the structure defined in equations (2.1) and (2.2), K is the diagonal loading factor,
      δ    D    ∈      R                            F          +          L                2            -      1      stands for the unit vector whose D+1 th element is 1, and other elements are all zeros, and R stands for real value.